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Thyroid cancer has a strong link to many types of environmental exposures, but asbestos may not be one of them.
In a cohort study of 4427 shipbreaking workers exposed to asbestos, 436 subjects were diagnosed with cancer and only 5 were diagnosed with cancer of the thyroid gland.[1] Other studies trying to link thyroid cancers to particular causes failed to draw an association to asbestos exposure .[2],[3]
On the other hand, other types of exposure to environmental or occupational hazards do seem to raise the risk of developing thyroid cancer. Exposure to pesticides, biocides and certain industrial chemicals, for example, increased the risk of developing thyroid cancer significantly.[4] For cumulative, long-term exposures, the risk more than doubled.
Radiation exposure also has a well-known connection to an increased risk of developing thyroid cancer.[5]
The crossover between occupational exposure to asbestos and other contaminants may be why some researchers guess that there may be a direct link between asbestos and thyroid cancer. Firefighters responding to the scene of the September 11, 2001 World Trade Center attacks had a relative risk of developing thyroid cancer nearly four times higher than the average U.S. firefighter.[6] Dust that resulted from the disaster contained not only asbestos but also glass fibers, pulverized cement, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and polycyclic aromatic hydrocarbons (PAHs).
Another confounding factor might be the association between asbestos and cancers of the throat (larynx) and esophagus. A review of nine large cohort studies found that there was substantial evidence of increased risk of developing laryngeal cancer after prolonged exposure to asbestos.[7] A minor dose-dependent effect was also observed, which means that heavier exposures potentially led to an even higher risk.
Despite this connection, the thyroid gland seems to remain separate from other organs in the neck when it comes to increased risk after exposure. Observed cases of co-occurring asbestos conditions, like mesothelioma, and thyroid cancer may be the result of exposure to other environmental hazards, like radiation or industrial solvents. Other factors, such as genetics, may also play a large role.
In conclusion, there may be a potential link to thyroid cancer and asbestos but the evidence just isn’t available yet. Patients diagnosed with thyroid cancer may want to look to other possible exposures or risk factors as the cause of their condition.
[1] https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0133128&type=printable
[2] http://www.em-consulte.com/en/article/270932
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4059396/
[4] https://oem.bmj.com/content/early/2017/02/15/oemed-2016-103931
[5] https://www.ncbi.nlm.nih.gov/pubmed/28225863
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5010035/
[7] https://www.ncbi.nlm.nih.gov/books/NBK20323/
